The purpose of the paper is to examine the effects of light, feeding and volatile fatty acid (VFA) injection on the behavior of rumination. Animals tested were four adult Saanen goats with rumen fistula. Ruminating behavior were more in night (dark environment), but were decreased during the evening (immediately after darkness). On the other, eating behavior was decreased ruminating behavior, but were increased before feeding, and it was not clear in detail of ruminating behavior during and before feeding. It was found that the circadian rhythms of ruminating behavior was influenced by normal daylight or artifical light-dark cycles in goats. More ruminating behavior of ruminants was increased in the night or darkness, and that suggest ruminant was a nocturnal animal. Ruminating behavior was influenced by injecting VFA or glucose into venous vein of goats. It was suggested that ruminating behavior was changed by blood compositions of the metabolites of ruminants. Because volatile fatty acid can not inter the brain barrier, they send the messages into ruminating center by ketone body (acetone) in the metabolites of VFA.Ruminating behavior was increased by acetone (ketone body). Acetate decreased ruminating behavior per a rumination (bolus) by injecting it into venous vein rumen. As mentioned above, it is suggested that VFA control the fermentation in rumen through the change of ruminating behavior influenced by VFA.